Multidrug-resistant gram-negative bacteria

The World Health Organization (WHO) has made its position unmistakably clear. Multidrug- resistant gram-negative bacteria are no longer an emerging concern but a dominant global health threat, with carbapenem resistance representing one of the most critical failures in contemporary antimicrobial therapy.

Organisms once treatable with last line of defence drugs such as meropenem and imipenem are now demonstrating sustained resistance across healthcare systems worldwide.

Cefiderocol (Fetcroja) — a new cephalosporin developed to be active against carbapenem resistant bacteria — was only approved for use in the EU in April 2020 and there are already studies suggesting that high rates of resistance in Cefiderocol are already being tracked.

From carbapenem resistant Klebsiella pneumoniae and Enterobacterales to highly resistant Acinetobacter baumannii and Pseudomonas aeruginosa, the organisms shaping the modern antimicrobial resistance landscape are increasingly defined by their ability to survive 
even the most advanced antibiotic intervention. The implications extend far beyond pharmacology. As therapeutic options contract, the global response is shifting toward prevention, containment, and environmental control.

The WHO now frames the fight against carbapenem resistance not simply as a drug development challenge, but as a systems level priority requiring coordinated clinical, microbiological and infrastructure-based action.

The shift from clinical responsibility and a sustainable policy on antibiotic management has now tangibly expanded to include built environmental management.

Favourable ecological conditions

Moist plumbing environments provide highly favourable ecological conditions for the persistence and amplification of gram-negative bacteria. Drains, sinks, and basins function not simply as passive waste pathways but as active microbial reservoirs capable of sustaining complex, structured communities over prolonged periods.

Several environmental characteristics make these sites particularly conducive to colonisation.

• Continuous moisture availability
  
Gram-negative organisms require hydrated environments for survival and metabolic activity. Plumbing systems maintain persistent dampness, often with intermittent stagnation that allows organisms to establish stable populations.

• Nutrient accumulation

  Organic matter from handwashing, clinical waste fluids, skin debris, food residues, and pharmaceutical compounds accumulates within pipework and trap systems. This provides a continuous nutrient supply that supports microbial growth and diversification.

• Temperature stability

  Ambient and lukewarm water conditions common in healthcare plumbing systems fall within optimal growth ranges for many gram-negative species, enabling continuous replication.

• Low mechanical disturbance in key zones

  U-bends, trap seals and horizontal pipe segments create areas of reduced flow where microorganisms can accumulate without regular flushing. 

• Aerosol generation and splash dispersion

  Water impact within contaminated drains can generate droplets and aerosols containing viable organisms. These may contaminate surrounding surfaces, equipment, and hands, creating transmission pathways into the clinical environment. 

• Antimicrobial exposure gradients

  Sublethal concentrations of cleaning agents, disinfectants, and residual antibiotics can accumulate within wastewater, creating selective pressure that favours resistant strains, including carbapenem resistant organisms. 

• Operational significance
  Drains and sink systems therefore act as persistent environmental reservoirs that can seed surrounding areas with clinically relevant gram-negative bacteria.

In healthcare, laboratory, and care environments, this combination of moisture, nutrients, protected growth structure, and dispersal mechanisms creates an ideal ecological niche for multidrug-resistant gram-negative organisms to persist, amplify and spread.

The impact of healthcare-associated infection on the NHS

Figures from a 2016/17 study state that, during the period of the study, approximately 653,000 healthcare associated infections occurred among 13.8 million adult admissions across the NHS in England alone.

These infections were linked to around 22,800 patient deaths. A further 13,900 infections were estimated among roughly 810,000 clinical staff working in direct patient care.

The total operational impact was substantial with healthcare associated infections accounting for about 5.6 million occupied bed days and resulted in approximately 62,500 staff absence days.

When specialist hospitals were also included, the estimated burden rose to around 834,000 infections. The wider NHS impact was associated with approximately 28,500 deaths and 7.1 million occupied bed days — representing around one fifth of all annual bed use, and close to 79,700 staff absence days.

Total costs were estimated at £2.7bn.

Clinical intervention is no longer a singular pathway to combatting anti-microbial resistance — there is now a clear need for mechanical intervention, supported by estates and facilities teams within the NHS.

Hygiene management within healthcare plumbing systems has moved from a maintenance function to 
a central component of infection prevention strategy. Drains, sinks, and basins are no longer viewed simply 
as wastewater conduits. They are recognised 
ecological reservoirs capable of sustaining, amplifying, and dispersing clinically significant gram-negative bacteria.

In modern healthcare environments where antimicrobial resistance is escalating, the management of these reservoirs has become an operational responsibility that directly influences patient safety, environmental contamination risk, and outbreak control.

At a microbiological level, sink infrastructure provides ideal conditions for persistent colonisation. Warmth, continuous moisture, intermittent nutrient loading, and protected surface structures create a stable habitat in which gram-negative organisms can establish complex biofilm communities. Once formed, these biofilms exhibit enhanced tolerance to chemical disinfectants and mechanical disturbance.

Organisms embedded within extracellular polymeric matrices can survive repeated cleaning cycles and repopulate surfaces rapidly after apparent removal. This persistence explains why plumbing systems can remain contaminated for extended periods even within highly controlled clinical environments.

The clinical relevance of these reservoirs is now well-documented. Healthcare associated outbreaks have repeatedly been linked to contaminated sinks and associated pipework, with multidrug-resistant gram-negative organisms detected in drain biofilms, surrounding surfaces, and patient environments. Sink systems are therefore not isolated microbial niches. They are integrated components of the environmental microbiome within patient care spaces.

Recent research has strengthened this understanding by directly demonstrating the movement of microorganisms from sink drains into the surrounding clinical environment.

Clear microbial continuity

A 2025 investigation of operational hospital rooms examined biofilms within patient room drains alongside droplets, aerosols, and nearby surfaces. Genetic analysis showed clear microbial continuity between drain biofilm populations and organisms recovered in the air and on surrounding surfaces. Viable opportunistic pathogens were identified in droplets and airborne particles generated during sink use, confirming that sink drains can function as active emission sources rather than passive containment structures.

This evidence has major implications for infection control. It confirms that plumbing contamination is not confined within pipework. Microorganisms established within the drainage system can enter the clinical environment through dispersal mechanisms triggered by normal sink operation.

Water flow, impact dynamics, and air displacement within the basin create conditions that mobilise microbial material from the drain and surrounding surfaces. These particles can deposit on worktops, equipment, and high touch areas or potentially remain suspended long enough to reach patient proximity.

Understanding the physical structure of the sink system is therefore essential. The traditional U-bend, or P-trap, has historically been designed for odour control and fluid retention. Its primary function is to maintain a water seal that prevents sewer gases from entering occupied spaces. However, from a microbiological perspective, this design introduces a set of unintended consequences that are increasingly difficult to ignore.

The U-bend potentially forms a region of permanent water stagnation. Organic matter, skin debris, clinical fluids, and detergent residues accumulate within this section of pipework. Limited flow velocity and protected internal surfaces support the development of dense microbial communities.

Over time, the trap becomes a stable growth chamber that is largely shielded from routine cleaning or flushing. Nutrient enrichment and limited disturbance allow biofilms to mature and diversify, often incorporating opportunistic pathogens associated with healthcare associated infection.

Once colonised, the U-bend becomes a persistent source of microbial release. Flow events passing 
through the trap generate turbulence and shear forces 
that dislodge biofilm fragments or suspend microorganisms within the water column. When water subsequently impacts the basin or drain surface, these organisms can be projected outward in droplets or aerosolised particles. Dispersion is therefore mechanically linked to the hydraulic behaviour of the plumbing system itself.

Dispersal: measurable rather than theoretical

More recent clinical observations reinforce this concern. The detection of genetically matched organisms in drain biofilms, droplets, and airborne samples confirms that dispersal is not theoretical but measurable within functioning healthcare environments. In practical terms, this means that routine handwashing or disposal of fluids can mobilise microbial populations from the U-bend and distribute them into the immediate clinical zone.

Aerosol and droplet formation is influenced by multiple interacting factors. Water velocity, angle of impact, basin geometry, and drain configuration all contribute to particle generation. Splashback from contaminated surfaces can extend beyond the sink perimeter, while smaller particles may remain suspended long enough to be inhaled or deposited at distance. Wastewater systems in general are recognised sources of bioaerosols capable of transporting microorganisms through the air, increasing the risk of environmental exposure.

For estates and facilities teams, these findings reframe the role of plumbing infrastructure. Drainage systems are not solely mechanical assets. They are microbiological environments that require structured risk management. Maintenance practices designed only to preserve function are insufficient when the system itself can act as a transmission pathway.

Effective hygiene management therefore requires a systems-based approach.

A systems-based approach

First, routine inspection and monitoring of high-risk sinks must be integrated into environmental infection control programmes. Locations with vulnerable patient populations, intensive water usage, or limited ventilation demand particular attention. Microbial surveillance of drains and trap systems can provide early indication of colonisation before clinical impact becomes evident.

Second, cleaning protocols must extend beyond visible surfaces. Basin disinfection alone does not address biofilm reservoirs within pipework. Interventions capable of reaching internal drainage structures are necessary to disrupt established microbial communities. Without direct control of the reservoir, surface decontamination becomes temporary and incomplete.

Third, sink usage practices should be evaluated in relation to infection risk. Disposal of nutrient rich fluids, inappropriate equipment washing, or high velocity water flow can increase microbial growth and dispersal potential. Behavioural controls, supported by training and operational policy, form an essential part of infrastructure hygiene.

Fourth, design considerations must be incorporated into refurbishment and new build projects. Basin geometry, water delivery systems, and drainage configuration influence both microbial accumulation and dispersion dynamics. Estates teams play a central role in specifying systems that minimise stagnation, reduce splash generation, and limit the persistence of biofilm reservoirs.

Fifth, mechanical systems must be understood as interconnected networks. Contamination within one section of pipework can migrate through shared drainage pathways. Isolated interventions may therefore be insufficient unless implemented across the system as a whole.

Finally, emerging technologies are now available that sit between the vertical sink drop and the U-Bend which have been proven to greatly reduce the likelihood of gram-negative bacteria from finding its way back to the open plug — thus reducing the risk of transmission in clinical areas.

For healthcare infrastructure management, this represents a definable and controllable risk domain. Addressing it requires recognition that infection prevention is not confined to clinical procedures or surface hygiene. It extends into the engineering of the built environment and the management of the systems that operate within it.

A potential solution

Mueller Europe has been working with an inventor, Dr. James Soothill MMBS, MD, FRCPath, a consultant microbiologist at Great Ormond Street Hospital to manufacture a mechanical modification, suitable for new build and retrofit projects.

Developed to address this built environment vulnerability, this drainage modification — along with the design and IP — are fully protected globally, to ensure the efficacy of the product as supplied to the NHS and broader healthcare markets.

This system introduces a long, continuously descending copper conduit positioned between the sink outlet and the conventional trap. Its function is not to eliminate microbial presence within the wider drainage network, but to interrupt the physical mechanisms that allow organisms resident within the trap to reach the sink outlet.

These types of mechanical intervention are based on the recognition that vertical water entry into trap water can generate upward splash and particle movement. This upward movement provides a pathway for microorganisms within contaminated trap fluid to ascend towards the sink outlet or upper waste pipe.

This type of design alters the geometry of fluid movement before it reaches the trap. Instead of allowing direct vertical entry, water descends along a sloped internal pathway that progressively redirects flow direction. This change in trajectory greatly reduces the likelihood that ‘splash’ or turbulent movement will travel back toward the outlet.

One key structural feature is the gradual change in gradient within the conduit; this redirects flow through a substantial change in direction before reaching the trap. This configuration interrupts linear splash trajectories, meaning droplets or particulate material travelling upward are more likely to impact internal surfaces rather than continue vertically.

The extended length and curvature of the conduit further increase the probability that suspended particles will settle or adhere before reaching the outlet.

The antimicrobial properties of copper

In addition to geometric flow control, these devices are constructed from copper. The antimicrobial properties of copper have been recognised for centuries and are supported by modern microbiological evidence demonstrating reduced survival of multiple bacterial species on copper surfaces and in copper containing water environments.

Incorporating copper into the drainage pathway introduces an additional inhibitory influence on microbial persistence and can potentially slow biofilm development within the conduit itself.

Clinical evaluations of this type of drainage modification have demonstrated measurable microbiological impact. A blind, randomised study conducted in a hospital outpatient setting compared sinks fitted with the device to matched controls with standard plumbing. Target organisms included clinically relevant gram-negative species associated with healthcare environments, such as Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia, and members of the Enterobacterales group.

Sinks incorporating the modified drainage pathway showed significantly lower counts of these organisms at the sink outlet over time, supporting the interpretation that the device limits movement of bacteria from trap reservoirs toward the basin interface.

Laboratory testing performed prior to clinical installation demonstrated a related mechanism. When bacteria were introduced into trap fluid, splashes reached the upper waste pipe in standard configurations but were not detected at equivalent locations when the modified drainage pathway was present. This finding supports the view that the primary effect arises from prevention of upward splash transmission from the trap.

From an infection prevention perspective, the significance of this approach lies in its focus on interrupting transmission rather than attempting complete eradication of microorganisms within the drainage system.

Given the difficulty of permanently decontaminating trap environments, physical isolation of the reservoir from the sink outlet represents a structurally based control strategy. By reducing the movement of gram-negative bacteria from trap water to areas of direct clinical interaction, this intervention addresses a defined environmental pathway associated with contamination risk.

In practical terms, these modifications represent an engineered intervention targeted at a recognised, specific weakness in conventional sink design. It acts by increasing separation between microbial reservoirs and the clinical environment, directly altering fluid behaviour that drives splash generation, and creating conditions less favourable for biofilm persistence in the upper drainage pathway.

Sustainability

As a mechanical intervention, this type of solution operates without any power, automated dosing system, or complex requiring any ongoing maintenance, thereby reducing energy demand and operational resource consumption. Its structural function is continuous and independent of user behaviour. Copper is durable and fully recyclable, supporting long service life and responsible material use. These features position the system as an infrastructure-based infection control measure that supports environmental management, resource efficiency, and long-term clinical resilience.

There is also a focus on the sustainable use of carbapenems, which is essential to preserving their clinical effectiveness over the long term.

Carbapenems are often reserved for severe infections and for organisms that cannot be treated with other therapies. Their value depends not only on their availability, but on how carefully they are used. Sustainability in this context means protecting their effectiveness so they remain reliable treatment options for future patients.

Careful prescribing is fundamental. Carbapenems should be used only when clearly justified by clinical need, supported where possible by microbiological evidence. Early diagnostic testing and rapid identification of the infecting organism allow treatment to be directed more precisely. This reduces unnecessary exposure and limits the selection pressure that encourages resistant strains to emerge.

To maintain a sustainable use policy for carbapenem prescribing, there needs to be a reduction in the requirement of use. This is turn can be managed by reducing the type of events requiring the use of such therapies by reducing the number of gram-negative bacteria outbreaks.

Preventing infection: a critical element of sustainable practice

Effective hygiene, environmental control, and safe management of water and drainage systems reduce the incidence of healthcare associated infection. When fewer infections occur, the need for advanced antibiotics such as carbapenems is reduced.

Sustainable carbapenem use extends beyond prescribing alone. It involves coordinated clinical decision making, effective infection prevention, and responsible management of healthcare environments, all aimed at preserving the effectiveness of these essential medicines for the future.

Bibliography

• World Health Organization: Global antibiotic resistance surveillance report 2025 www.who.int/publications/i/item/9789240116337
• The Journal of Hospital Infection — Tuba Drain technology. www.sciencedirect.com/science/article/abs/pii/S0195670124003621
• Aerosol-based exposure to opportunistic pathogens originating from hospital sink drains. www.sciencedirect.com/science/article/abs/pii/S0196655325007011
• Resistance profiles of carbapenemase-producing Enterobacterales in a large centre in England: are we already losing cefiderocol? https://academic.oup.com/jac/article/80/1/59/7879525
• ECDC — Rapid risk assessment — Carbapenem-resistant Enterobacterales — third update. www.ecdc.europa.eu/en/publications-data/carbapenem-resistant-enterobacterales-rapid-risk-assessment-third-update
• American Society for Microbiology – A Large, Refractory Nosocomial Outbreak of Klebsiella pneumoniae Carbapenemase-Producing Escherichia coli Demonstrates Carbapenemase Gene Outbreaks Involving Sink Sites Require Novel Approaches to Infection Control. https://journals.asm.org/doi/10.1128/aac.01689-18
• Cost of Nosocomial Outbreak Caused by NDM-1—Containing Klebsiella pneumoniae in the Netherlands, October 2015—January 2016. https://www.researchgate.net/publication/319424548_Cost_of_Nosocomial_Outbreak_Caused_by_NDM-1-Containing_Klebsiella_pneumoniae_in_the_Netherlands_October_2015-January_2016